The aim of this study was to compare the surface discoloration of polished and celluloid strip-finished composite surfaces in microhybrid type composites and to determine whether or not the discoloration of a celluloid strip-finished composite surface is reduced if oxygen inhibition on the surface can be prevented. The composite surfaces were celluloid-strip finished (group 1), polished (group 2), or celluloid-strip finished under nitrogen gas purging (group 3). Z100, Spectrum, and Aelitefil were used as the test materials. After each surface treatment, the samples were stored in 37°C distilled water for 24 h and placed in a disclosing solution (0.2% Erythrosin, pH 7.0) for 7 days in the dark. A computer controlled spectrophotometer was used to determine the CIELAB co-ordinates (L*, a*, b*). For each composite, the degree of discoloration among the groups was compared with a one-way ANOVA test. A Dunnett's t-test was then performed to compare the colour change in group 1 with that of group 2 or group 3. In all materials, there were no statistical differences in the surface discoloration between group 1 and group 2. In the Aelitefil and Spectrum test materials, the samples in group 3 showed a lower level of discoloration than the those in group 1. In Z100, there was no statistical difference. In microhybrid composites, there was no difference in surface discoloration between celluloid strip-finished and the polished surface. Nitrogen gas purging during the polymerization process on the celluloid strip-finished composite surface might be useful for reducing the discoloration celluloid strip-finished surface in microhybrid composites.
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